1. Field of the Invention
The present invention relates to an electrical unit for providing electrical functions to a user, and more particularly relates to an electrical box that enables efficient installation and replacement of electrical units of a building.
2. Discussion of the Background
In providing electrical power to commercial and residential buildings, a main power line typically carrying 100-200 Amps of 220 VAC single phase power enters the building from an electric company power grid and is connected to a service box that distributes power to the entire building. In the service box, the 220 VAC power is center tapped with a neutral return to provide two 110 VAC sources of opposite polarity and ground terminal connected to the earth.
In the service box, power from the main power line is divided into branch circuits each of which typically provides 110 VAC power circuit breakered at 15 to 25 Amps to several plugs, switches, and/or other electrical units located in different areas of the building. In providing such branch circuits, multi-conductor electrical cable must be routed from a branch circuit breaker in the main service box to electrical boxes that contain each of the electrical units in the branch circuit. The multi-conductor cable used to route the branch circuits typically includes a white insulation neutral wire, a black insulation hot wire, and a bare or green insulation ground wire to carry 110 VAC throughout the building. In branch circuits, in which 220 VAC are used, a red insulation alternative hot wire is also provided in the multi-conductor cable, and higher currents are allowed for certain high power appliances, such as stoves, ovens, air conditioners, heaters and clothes dryers.
Current practice in wiring a branch circuit is to route individual segments of the multi-conductor electrical cable from the interior of one electrical box to the interior of a subsequent electrical box in the circuit. When all electrical boxes are connected with cable segments, the free ends of the cable segments at the interior of each box are connected to complete the branch circuit. In completing the branch circuit, the outer insulation sheathing is first stripped off of each free end of cable to expose the internal electrical wires, and the insulation is then stripped off of the end of each wire to expose the copper conductor of the wire. The bare conductors of each wire are then connected by use of twist-on connectors or by connecting the conductor to a switch, plug, or other electrical unit in the box and the cables are folded within the interior of the box to make room for the electrical unit.
Similarly, when a new load, such as an electrical outlet is added to an existing electrical circuit, wires of the existing circuit must be spliced into and reconnected by use of the added load. Specifically, in adding a load, the electrician must first cut an opening in the finished wall to reveal the existing electrical cable which is then cut to provide two ends of the cable which are inserted into an electrical box used for housing the electrical outlet to be added. In situations whereby the electrical cable is not long enough that the ends of the cable can reach the interior of the new electrical box, it may be necessary for the electrician to install at least one junction box to extend the ends of the cable. The ends of the cable are then prepared and the internal wires are stripped as described above. The wire ends are reconnected through the electrical unit in the box to complete the circuit, and the wires are folded into the new box as discussed.
These conventional methods of wiring a building, however, present a number of problems to the electrician and homeowner. First, from the standpoint of the electrician, the effort it takes to cut and route cable segments between electrical boxes, and then to strip and reconnect the internal wires of the cable using the above-described method is very time consuming and labor intensive. In addition, in installing a new electrical outlet, existing wires may have to be extended by use of a junction box requiring extra time. In addition, because multi-conductor electrical cables have three or four individually insulated conductors bound together by an outer sheathing, the cable is stiff and difficult to fold into the electrical box in such a way that plugs, switches, and other electrical units will have enough room to fit in the box. This creates greater inefficiency and makes it difficult for the electrician to sufficiently align all of the plugs and/or switches in a multi-ganged box so that a cover plate can be placed over the electrical unit and box.
In addition to the above-described efficiency problems, a significant amount of wire is wasted in routing all branch circuits from one main service box to each branch circuit region that the service box is to power. For example, providing power to the top floor of a large home may require two 15 Amp branch circuits in which case two multi-conductor electrical cables need to be routed from the main service box located in the basement, for example, to the area powered by each circuit. Distributed service panels that may resolve this problem have not been feasible in such situations due to their expense and large size that is not desirable for living space. Although to a lesser extent, electrical wire is also wasted when cable ends must be extended to reach the interior of a new electrical box when adding a load to an existing circuit.
From the home or building owner""s standpoint, with the hundreds of electrical connections inside even a small house, the complicated method of cutting and stripping cables and internal wires as described above is likely to result in at least one poor connection that will eventually fail. The possibility of a poor connection is also present for the addition of new outlets. The failure of such a poor connection can be as benign as denying electrical service to all downstream electrical boxes in the circuit or as disastrous as causing a house to bum down. Moreover, nicking, or cutting into, of a conductor of each wire may occur each time insulation is cut off the wire to expose bare copper for the connection. This reduces the wire surface area available for carrying electrical current and can cause localized overheating, with the potential to start a fire. Reduced surface area may also cause a significant voltage drop that slows down motors, dims lights, or affects the operation of voltage sensitive appliances.
In addition, because the multi-conductor electrical cable enters each electrical box and must be connected to the electrical unit and folded within the box, space inside each electrical box is limited thereby limiting the number and sophistication of features offered by the electrical units used with the electrical box. Finally, replacement of electrical units may be problematic for the above-described system because it is common for electrical wires to break when being removed from the electrical unit to be replaced. This shortens the length of wire within the electrical box making it difficult or impossible to connect the new electrical unit without extending the length of wire with a splice.
Based on the foregoing, there is a clear need for an electrical unit that provides safe and reliable electrical functions for a user in a home and/or commercial building.
There is also a need for an electrical unit that mates with an electrical box without the use of electrical wires that occupy space within the electrical box.
Finally, there is a need for an electrical unit having sophisticated features yet is easy to align within the electrical box so that a decorative cover can be attached to the electrical box.
According to one aspect of the invention, an electrical unit for mating with an electrical box is provided. The electrical unit includes a body having a device surface and a mating surface. An electrical device configured to provide an electrical function to a user is arranged on the device surface, and neutral and hot contacts configured to receive respective neutral and hot conductive members of an electrical box are mounted on the mating surface. The electrical device may be any one of an outlet, a switch, circuit breaker, or any combination of these devices. In addition to the neutral and hot contacts, ground and alternative contacts may be provided on the mating surface and each contact may be a rigid electrical socket oriented in a keyed configuration so as to electrically connect to the respective conductive members without the use of connecting wires when the electrical unit is mated with the electrical box. The electrical unit may include a mating screw which, when tightened in a screw hole of the electrical box, causes the electrical unit to mate with the electrical box, and a non-conductive member mounted on the mating surface which prevents the electrical unit from mating with a non-compatible electrical box.
According to another aspect of the present invention, the electrical unit includes a means for containing electrical circuitry, the means having a device surface and a mating surface. A means for providing an electrical function to users is arranged on the device surface, and means for receiving neutral and hot conductive members of an electrical box are mounted on the mating surface. The means for providing an electrical function may be any one of a means for providing electrical power, means for switching electrical power, means for interrupting electrical power, or any combination of these means. In addition to the means for receiving neutral and hot conductive members, means for receiving ground and alternative hot conductive may be provided on the mating surface, and each of these means may be in a keyed configuration so as to electrically connect to the respective conductive members without the use of connecting wires when the electrical unit is mated with the electrical box. The electrical unit may include means for fastening the electrical unit to the electrical box, and means for preventing the electrical unit from mating with a non-compatible electrical box.
In still another aspect of the present invention, a method of connecting an electrical unit that provides an electrical function to an electrical box is provided. The method includes aligning neutral and hot contacts of the electrical unit with respective neutral and hot conductive members of the electrical box, and press fitting the neutral and hot contacts to mate with the respective conductive members such that electrical contact is made between the electrical unit and the electrical box without the use of electrical wires. The method may also include aligning a mating screw of the electrical unit with a screw hole in the electrical box so that press fitting is accomplished by turning the mating screw in the screw hole such that the electrical unit is pulled into mating with the electrical box.